This invention relates to medical instruments.
More particularly, the present invention relates to devices for spinal fixation
In a further and more specific aspect, the instant invention concerns positioning and placement of pedicle screws.
Injuries to the spinal column have always been numerous and debilitating. Only recently have techniques been developed to reduce effects of injuries and wear on the vertebrae. Spinal fixation employing screws inserted into the pedicles of the vertebrae is a well accepted technique. The force nucleus of the normal vertebrae is located at the base of the superior process at a point where the ridge on the pars interarticularis, the ridge on the superior facet, and the ridge on the transverse process all converge. Opening the cortical bone at this point permits access to the intermedullary canal of the pedicle through which the screw passes into the vertebral body. Generally, screws are inserted into a number of vertebrae and fix plates in position for stabilization of a portion of the spinal column.
Each screw is inserted by first locating the proper area either visually or by the use of a probe. When the proper location (force nucleus) is located, an opening is typically formed in the cortical bone using a rongeur or gouge. Once a portion of the cortical bone has been removed, a pedicle probe is employed to probe the pedicle. The probe is inserted with its tip perpendicular to the horizontal plane. A gentle back-and-forth or wiggle motion is used to advance the probe through the cancellous bone within the pedicle. It is desirous that the angled tip of the probe follow the cancellous tube of bone to the vertebral body. However, often the probe will sharply exit the pedicle. If this occurs, a ball tip probe must be employed outside the pedicle to determine if the probe has indeed exited the pedicle. This can be a serious problem if the probe exits into the vertebral foramen. Often the physician will manipulate the probe in such a manner as to insure that an exit does not occur into the vertebral foramen. This, however, often has the result of over compensation and an exit in a different location.
After the probe reaches the vertebral body, the probe is withdrawn and a marker is inserted. Intraoperative x-rays are taken to confirm positioning, before the screws are inserted. After the exploratory probe has been completed, each pathway must be widened with a tap of appropriate dimensions. The pedicle screw is then positioned.
While effective, current placement of pedicle screws is time consuming due to the number of steps, including penetrating the cortex, probing the pedicle, confirming the positioning, tapping the pathway, and inserting the screw. Furthermore, the skill needed to perform this procedure, particularly the step of probing, is very great. While following the path of least resistance, namely the cancellous tube through the pedicle, sounds straight forward, it is very difficult. The cancellous tube is bone, and although less resistant than the cortex, still requires pressure to force the probe through. A great deal of xe2x80x9cfeelxe2x80x9d and control is needed to avoid exiting the pedicle. Even with highly skilled individuals, many exits occur. While generally not injurious, this slows the process even more. There is also the chance of injury to the spinal cord and/or nerve roots if the exit occurs into the vertebral foramen. The high level of skill required and the time required translates into increased expense.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide a new vertebral drill bit and inserter.
Another object of the invention is to provide a vertebral drill bit which is self guiding.
And another object of the invention is to provide a vertebral drill bit which will reduce exits from the pedicle.
Still another object of the present invention is to provide a vertebral drill bit which can be employed to confirm positioning.
Yet another object of the invention is to provide a vertebral drill which is relatively quick and easy to use.
Briefly, to achieve the desired objects of the instant invention in accordance with a preferred embodiment thereof, provided is a vertebral drill bit for forming a pathway through a pedicle into a vertebral body. The drill bit includes a cutting shank having a first end and a second end and a generally uniform diameter therebetween, an attachment head at the first end of the cutting shank and a tip at the second end of the cutting shank. Also provided is a point at which the diameter of the cutting shank at the second end begins to get smaller to form the tip. A flute is formed in the cutting shank and extends from the first end to the tip. An edge of the flute from the first end to proximate the point is sharp for cutting, and edges of the flute from the point to the tip are rounded.
Also provided in another embodiment is an inserter for coupling the drill bit to a drill. The inserter includes a chuck end and a receiver end.